The filming, which is taking place by a lake in Wilmington, N.C., is McCarthy’s directorial debut. The fired mother, believed to be in her 20s, had brought along her 4- to 5-year-old son for the day's filming, sources said.

Witnesses said the mother struggled to control the boy most of the day in the gathering of more than 200 extras. Extras for the movie are being paid $58 a day.

The mother’s chiding continually disrupted the set. After struggling to control the boy, the mother apparently lost her temper and jerked the youngster up in the air by a wrist.

After watching the incident, sources said McCarthy had a personal assistant fire the woman. The mother's identity was not disclosed, and reps for McCarthy had no immediate comment.

McCarthy is co-directing the film with her husband Ben Falcone; it's slated to hit theaters July 2, 2014.

Commenters around the Web lauded McCarthy, who is a mother of two, for taking time out of her role as director not only to restore order to the set, but also to make a point about children.

“Everyone should applaud Ms. McCarthy and thank her for doing her civic duty,” said one commenter at the Huffington Post. “Too many people turn their heads and ignore child abuse! If someone is bold enough to mistreat a child in public, imagine the horror that happens behind closed doors. Thank you Melissa for standing up and displaying your values! This is a woman we need to see and hear more from.”

Other commenters, though, took the side of the young mother. Commenters claimed the mother needed parenting assistance more than the embarrassment of being fired.

“It is easy to speak harshly of the young mother when you don't know what was going on,” said one commenter at London’s Daily Mail. “The set or shoot involved using children too. While I'm against abuse, I am for discipline. No one knows how hard it may be or has been on that young mother. If Melissa wanted her fired, why didn't she do it herself?? Why not try to help the young mother?”

Melissa McCarthy reportedly fired an extra from the set of “Tammy” on Monday when McCarthy saw the young mother “manhandle” her child. McCarthy is playing a woman fired from her job in the film project.